Congestive heart failure (CHF) now afflicts over 4 million Americans, and at least 400,000 new cases are found each year. The 5-year mortality of patients newly diagnosed with congestive heart failure is fifty percent, despite the best medical efforts. Most congestive heart failure cases are the result of impaired systolic function due to ischemic heart disease or idiopathic dilated cardiomyopathy. Impaired systolic function, in turn, can result in interventricular dyssynchrony. Interventricular dyssynchrony occurs when there is a delay between right ventricular (RV) and left ventricular (LV) activation. Interventricular dyssynchrony is particularly likely in the presence of left bundle branch block, in which RV contraction will precede LV contraction, leading to decreased LV ejection fraction.
Physiological benefits of CRT have included improved autonomic function, partial reversal of LV remodeling, improved LV function, and improved myocardial efficiency as well as decreased mitral regurgitation (MR). Echocardiographic strain-mapping studies have suggested that the improvement in MR may be due to restoration of synchronized papillary muscle function. Clinical trials have shown improved functional class, quality of life, and exercise tolerance. A meta-analysis of randomized, controlled trials that collectively evaluated a total of 1634 patients found that CRT was associated with a 51% reduction in death from progressive heart failure, a 29% reduction in heart failure hospitalization, and a trend toward a reduction of all-cause mortality. Despite these promising findings, CRT is still associated with limitations. A substantial proportion (25% to 30%) of patients who undergo CRT may not respond to therapy.